Method of testing the point bearing capacity of a pile shell



Aug. 4, 1936. E. D. WATT 2,050,217

METHOD OF TESTING THE POINT BEARING CAPClTY OF A PILE SHELL original Filed April 5, 1933 2 Sheets-Sheet l III EL; @5 //f fw E. D. WATT Aug, 4, 1936.

METHOD OF TESTING THE POINT BEARING CAPACITY OF A PILE SHELL Original Filed April 5, 1935 2 Sheets-Sheet 2 Patented Aug. 4, 1936 U N l TED STAT ES PATENT OFFICE Elihu D. Watt, Plainfield,

mond Concrete Pile Co N. J., assigner to Raympany, New York, N. Y.,

a corporation of New Jersey Original application April 5, 1933, Serial No.

Divided and this application August Y 31, 1934, Serial No. 742,459

1 Claim.

This application is a division of my co-pending application, Serial No. 664,517, and pertains to the manufacture of concrete piles in which the thin, comparatively delicate shell used as a permanent 5 mold for the concrete is surrounded and protected during the driving operation by a heavy tubular casing which is subsequently removed.

An object of the present invention is to disclose apparatus for testing the point resistance of the shell after driving, and prior to lling it with concrete.

Further and other objects and advantages will be apparent from the specification and claim, and from the accompanying drawings which illustrate what is now considered the preferred embodiment of the invention.

Fig. l shows a shell casing and driving core at conclusion of the driving operation, the driving core being provided with a drop hammer within its lower end.

Figs. 2 and 3 show modifications of the lower end of Fig. 1.

Fig. 4 is a view similar to Fig. 1, but with a hydraulic plunger in the driving core in place of the drop hammer.

Fig. 5 shows a modification of the lower end of Fig. 4.

The pile shell, designated 20, is provided at its lower end with a welded-on sheet steel boot 22, and the casing is designated 28. The casing is provided at its upper end with a ring 30 having hooks 32 adapted for engagement by links 34 hanging from the drive head. During the driving operation collar 30 is in contact with the under surface of the drive head and after the driving is finished, hooks 32 serve-as convenient means for engaging the casing to withdraw it from its position about the shell.

Boot 22 is provided near its top with a circumferential bead 38 and above the bead is an angle ring 40 fitted as shown snugly around the top of the boot. The bottom of casing 28 engages ring 40 as shown and the ring serves during driving to prevent entrance of material between casing and shell. Also, during driving, ring 40 serves as a plow in advance of the casing.

After the driving operation is finished, the drive core and casing may be withdrawn, leaving shell 20, boot 22 and ring 40 in place. During withdrawal, any attempt of shell 20 to follow the casing and core is usually prevented by engagement of the surrounding earth With ring 40, which in turn engages bead 38 on the boot.

During the driving of a pile shell by the method described above, two kinds of resistance are encountered, one being the friction of the casing, and the other being the point bearing or resistance of the boot, or bottom of the shell. After the pile is completed, the carrying capacity represented by the point bearing remains, but the friction of the ground on the sides of the pile may be largly lost, due to the fact that the withdrawal of the casing leaves a void between shell and ground, and the void may not completely close.

This makes it important to know whether or not the point bearing is able to carry the load. The present invention discloses means for testing the point bearing capacity of the pile by applying a known force to the boot after it is driven. One method is shown in Figs. 1, 2 and 3, in which l5 a drop hammer 58 is inserted in the bottom part of the drive core 52, the top of the hammer contacting with shoulder 54 of the core. After the driving operation is finished, the core is raised possibly two or three feet and the hammer is 20 operated by means of cable 56 passing over sheave 58 in drive head 59, the driving core acting as a guide for the hammer. If the bearing capacity of the point be found insulcient, the drop hammer may be operated until suitable carrying ca- 25 pacty is obtained. The drop hammer may also be used to assist in holding down the shell during withdrawal of core and casing. The hammer is finally withdrawn by its cable 56.

Fig. 1 shows both drop weight and core in con- 30 tact with boot 22, thus permitting the hammer to contact with a very limited area of the boot.

Fig. 2 shows a modification permitting greater contact between hammer and boot. Shell 20 and boot 60 are attache-d to a step ring 62, and the 35 hammer 64 is so shaped as to bear on the step ring as well as on the inner surface of boot 60. During the driving operation core 66 is raised to serve as a guide for the hammer.

Fig. 3 shows a modification in which an anvil 40 68 remains in contact with boot 60 and step ring 62, the anvil being driven by hammer lll. The anvil is'connected to the hammer by a pin l2 having a head 14 with which split collar 16 (fast in the hammer) engages when the hammer is 45 raised out of the shell.

Figs. 4 and 5 show the use of a hydraulic plunger to test the point bearing capacity of th-e pile and also to lift the core and casing by reaction against the point of the shell. During the driving 50 operation the parts are assembled as in Fig. 4, shell 20, boot 22, casing 28, bead 38 and angle ring 40 being the same as before. In this modification, however, the drive core 8U is bored to receive a plunger 82 adapted to be forced down- 55 wardly relatively to the core when uid under pressure is admitted to space 84 between plunger 82 and drive head 86. For convenience, plunger 82 is usually hollow, and its lower end has a head 88 seating in concrete 90 with which boot 22 is lled (Fig. 4). A modified arrangement of plunger head is shown in Fig. 5, in which no concrete is used in the boot, Contact being made directly with the boot by a suitably shaped head 92.

After driving, fluid is forced through passage 95 into space 84. This fluid tends to lift the core and casing and to force the shell further into the ground. If the friction between ground and casing, aided by a load placed on drive head 86, is suiiicient, the force acting downwardly on the point will be sufficient to impose a satisfactory test load (as measured by a pressure gauge) on the pile point. If the point resistance is below requirements, the shell can be pushed down by the plunger until suicient point resistance is obtained. Core and casing are finally raised by still further increasing the fluid pressure or by removing load from the drive head, or both. This reaction arrangement eliminates all possibility of the shell rising while core and casing are being withdrawn.

The plunger is withdrawn into the core by cable 94 passing between shell 2U and core 80 through a passage in head 88 or 92 and over sheaves 96 in drive head 86.

It is to be understood that the invention is not limited to the specic embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as dened by the following claim.

I claim:-

The method of testing the point bearing capacity of a pile shell having a boot on its lower end, comprising protecting the shell from contact with the ground, and applying a known downward force to the inside of the boot.

ELIHU D. WATT. 

